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I was wondering, if two cars (A and B) are going at different velocities let's say A=90km/h, B=80km/h then if we add the two speeds we get 170km/h meaning they are relative to each other.

But if one of the cars were going at the speed of light and the other at 90km/h it's impossible to add them because nothing can go faster than the speed of light meaning they are/aren't relative.?

So my question is: is light relative?

user555076
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  • Check out the basics of Special Relativity and you will understand your question. And read about some related thought experiments. You are free to ask the conceptual doubts while you study them. – N.S.JOHN Feb 07 '16 at 10:23

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velocities don't add up like A + B = C. This is only approximately true in the limit of every day perception. You have to consider your coordinate frames relative to each other if you approach relativistic (meaning a fraction of the speed of light) velocities.
$s = \frac{u + v}{1 + \frac{u v}{c^2}}$ would be the added velocity s of two objects moving relative to each other with velocity u and v respectively. For more information see Lorentz transformation

rtime
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